1. Field of the Invention
The present invention relates generally to clutch systems for industrial transmissions an more specifically to an industrial transmission that has a balanced clutch system that resists self-engaging.
2. Discussion of the Related Art
It is known that industrial transmissions are suitable for numerous power transmitting applications. Recently, industrial transmissions have been implemented more frequently in the well drilling and other energy production industries. For example, in light of concerns regarding hydrocarbon availability, efforts have been made to increase productivity of hydrocarbon wells, in terms of efficiency and overall production. One known technique for increasing productivity of a hydrocarbon well is to stimulate the well by hydraulically (or using other fluids for) fracturing the subterranean geological formation of the well in a manner that increases permeability and therefore flow rate of the well, increasing its productivity.
Many efforts have been made to provide machines and systems that incorporate transmissions and are suitable for such well-stimulating fracturing tasks. Accordingly, machines and systems (referred to hereinafter as “fracturing machines”) have been introduced for pumping fluids into hydrocarbon wells. Such machines typically have an internal combustion engine that drives a transmission which, in turn, drives a hydraulic pump to generate pressures that are large enough to fracture the underground formations, increasing well productivity. As power requirements for fracturing procedures have increased over time, so have the demands on the transmissions in the fracturing machines.
Use of these fracturing machines can require them to be operated for extended periods of time. During such extended periods of use, the transmission may be required to selectively engage or disengage various transmission or PTO (power take off) outputs, so as to direct power from the engine toward one or more well-drilling or pumping related tools or accessories.
Typical transmissions used in fracturing machines include hydraulically actuated clutches. The clutches are mounted on shaft assemblies that, at times, rotate when the clutch is disengaged. The clutch itself, or components thereof, may also rotate when disengaged. With the shaft and/or clutch rotating while the clutch is disengaged, oil volume captured in a clutch piston cavity establishes a centrifugal pressure head that is proportionate to shaft rotational speed. This centrifugal pressure acts on the clutch piston, actuating the clutch piston toward its engaged position and thereby self-engaging or auto-engaging due to the centrifugal oil pressure head. Self-engagement of clutches can be problematic whether they are fully engaged or partially engaged so as to create a rotational drag or slipping condition within the clutch that can create heat and reduce the use life of various clutch components.
Some efforts have been made to alleviate clutch self-engagement that is caused by centrifugal head pressure. Some attempts are only able to prevent clutch self-engagement at certain narrowly defined operational (rotating) speeds. Typical clutch self-engagement attenuating configurations evacuate pressure behind the clutch piston, for example, by draining oil from the clutch piston cavity that is behind the clutch piston. Draining the clutch piston cavity in this way can cause actuation delays when trying to move the clutch piston. For example, prior art clutches can experience a clutch disengagement delay because it takes time to evacuate oil from the clutch piston cavity. These prior art clutches can also experience a clutch engagement delay because the clutch piston cavity has to be sufficiently replenished before a hydraulic pressure can build therein, to an extent needed to hydraulically push the clutch piston.
The prior systems fail to provide a solution to the problem of preventing clutch self-engagements while maintaining quick actuation response characteristics of clutches.
Accordingly, there was a need for a clutch system that can mitigate tendencies of clutch self-engagement across a wide range of operating speeds, while having quick actuation, engagement and disengagement characteristics. A solution which minimizes complexity without compromising integrity was preferred.